ISAM Appliance Networking Changes

In ISAM v8.0.1.2, some fairly significant changes were introduced to the Management of the ISAM appliance networking interfaces. The update removed the concept of separate NICs for Application and Management interfaces and instead bound those concepts to an IP Address. It added support for VLAN tagging on packets, and provides a number of enhancements around routing and DNS management.

Scott Exton one of the lead programmers on the ISAM appliance wrote his own blog post discussing a number of the changes and the rationale behind them:


One of the most notable differences that punters will notice in the updated version is that the appliance no longer allows separate physical NICs (or virtual NICs) to span the same subnet. This is a fairly big deal for many of our customers who have enjoyed putting their management interface and their application interfaces on the same subnet in test environments etc.

Having a single subnet which spans multiple interfaces is a big no-no in general networking terms, and this is in no way specific to the ISAM appliance.  If you google this concept you will see that it is universally discouraged.

Scott mentions that this is a universally discourage concept, and I wanted to look into this further, here are some articles I found from other vendors on the concept:


If you configure a Windows-based computer that has more than one network adapter on the same physical network and protocol subnet, you may experience unexpected results.

National Instruments:

Using multiple NICs on the same subnet is the #1 cause of connectivity issues on multi-NIC systems.

Many other forum discussions (and troubleshooting unpredictable results) with the following search string:

So in essence, the ISAM development team have pushed us in this direction for a reason, and the number of support calls to debug network level issues has justified this change. In the meantime, we all need to adjust, and take advantage of the fact we can run everything on a single NIC interface!

One Interface to do it all! Here I have two Management IPs and one Application IP on the same NIC.


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